The Plasma technology now makes it possible to achieve flat colour panel of large size (out of the CRT limitations) and with very limited depth without any viewing angle constraints.
Referring to the last generation of European TV, a lot of work has been made to improve its picture quality. Consequently, a new technology like the Plasma one has to provide a picture quality as good or better than standard TV technology. On one hand, the Plasma technology gives the possibility of “unlimited” screen size, of attractive thickness, etc. But on the other hand, it generates new kinds of artefacts, which could reduce the picture quality.
Most of these artefacts are different as for TV pictures and that makes them more visible since people are used to seeing old TV artefacts unconsciously.
The artefact, which will be presented here, is called “dynamic false contour effect” since it corresponds to disturbances of grey levels and colours in the form of an apparition of coloured edges in the picture when an observation point on the PDP screen moves. The degradation is enhanced when the image has a smooth gradation like a skin. This effect leads to a serious degradation of the picture sharpness, too.
FIG. 1 shows the simulation of such a false contour effect on a natural scene with skin areas. On the arm of the displayed woman are shown two dark lines, which e.g. are caused by this false contour effect. Also in the face of the woman such dark lines occur on the right side.
In addition, the same problem occurs on static images when observers are shaking their heads and that leads to the conclusion that such a failure depends on the human visual perception and happens on the retina.
Some algorithms are known today, which are based on motion estimation in video pictures in order to be able to anticipate the motion of the critical observation points to reduce or suppress this false contour effect. In most cases, these different algorithms are focused on the sub-field coding part without giving detailed information concerning the motion estimators used.
In the past, the motion estimator evolution was mainly focused on flicker-reduction for European TV pictures (e.g. with 50 Hz to 100 Hz upconversion), for proscan conversion, for motion compensated picture encoding like MPEG-encoding and so one. For that purpose, these algorithms are working mainly on luminance information and above all only on video level information. Nevertheless, the problems that have to be solved for such applications are different from the PDP dynamic false contour issue, since the problems are directly linked to the way the video information is encoded in plasma displays.
A lot of solutions have been published concerning the reduction of the PDP false contour effect based on the use of a motion estimator. However, such publications do not mention the topic of motion estimators and especially its adaptation to specific plasma requirements.
A Plasma Display Panel (PDP) utilizes a matrix array of discharge cells that could only be “ON” or “OFF”. Also unlike a CRT or LCD in which grey levels are expressed by analog control of the light emission, a PDP controls the grey level by modulating the number of light pulses per frame. This time-modulation will be integrated by the eye over a period corresponding to the eye time response.
When an observation point (eye focus area) on the PDP screen moves, the eye will follow this movement. Consequently, it will no more integrate the light from the same cell over a frame period (static integration) but it will integrate information coming from different cells located on the movement trajectory and it will mix all these light pulses together which leads to a faulty signal information.
Today, a basic idea to reduce this false contour effect is to detect the movements in the picture (displacement of the eye focus area) and to apply different type of corrections over this displacement in order to be sure the eye will only perceive the correct information through its movement. These solutions are described e.g. in EP-A-0 980 059 and EP-A-0 978 816 that are published European Patent Applications of the applicant.
Nevertheless, in the past, the motion estimator evolution was mainly focused on other applications than Plasma technology and the aim of a false contour compensation needs some adaptation to plasma specific requirements.
In fact, standard motion estimators work on video level basis and consequently they are able to catch a movement on a structure appearing at this video level (e.g. strong spatial gradient). If an error has been made on a homogeneous area, this will have no impact on standard video application like proscan conversion since the eye will not see any differences in the displayed video level (analog signal on CRT screen). On the other hand, in the case of a plasma screen, a small difference in the video level can come from a big difference in the light pulse emission scheme and this can cause strong false contour artefacts.
Invention
It is therefore an object of the present invention to disclose an adapted standard motion estimator for matrix displays like plasma display appliances. That is the key issue of this invention, which could be used for each kind of Plasma technology at each level of its development (even if the scanning mode and sub-field distribution is not well defined).
According to claim 1 the invention concerns a method for processing video pictures for display on a display device having a plurality of luminous elements corresponding to the pixels of a picture, wherein the time duration of a video frame or video field is divided into a plurality of sub-fields (SF) during which the luminous elements can be activated for light emission in small pulses corresponding to a sub-field code word which is used for brightness control, wherein to each sub-field a specific sub-field weight is assigned, wherein motion vectors are calculated for pixels and these motion vectors are used to determine corrected sub-field code words for pixels, characterized in that, a motion vector calculation is being made separately for one or more colour component (R,G,B) of a pixel and wherein for the motion estimation the sub-field code words are used as data input, and wherein the motion vector calculation is done separately for single sub-fields or for a sub-group of sub-fields from the plurality of sub-fields, or wherein the motion vector calculation is done based on the complete sub-field code words and the sub-field code words being interpreted as standard binary numbers.
Further advantageous measures are apparent from the dependent claims.
The invention consists also in advantageous apparatuses for carrying out the inventive method.
In one embodiment the apparatus for performing the method of claim 1, has a sub-field coding unit for each colour component video data, and corresponding compensation blocks (dFCC) for calculating corrected sub-field code words based on motion estimation data, and is characterized in that, the apparatus further has corresponding motion estimators (ME) for each colour component and that the motion estimators receive as input data the sub-field code words for the respective colour components.
In another embodiment the apparatus for performing the method of claim 1, has a sub-field coding unit for each colour component video data, and is characterized in that, the apparatus further has motion estimators for each colour component and the motion estimators are sub-divided in a plurality of single bit motion estimators (ME) which receive as input data a single bit from the sub-field code words for performing motion estimation separately for single sub-fields and that the apparatus has a corresponding plurality of compensation blocks (dFCC) for calculating corrected sub-field code word entries.
In a third embodiment the apparatus for performing the method of claim 1, has a sub-field coding unit for each colour component video data, and is characterized in that, the apparatus further has motion estimators for each colour component and the motion estimators are single bit motion estimators which receive as input data a single bit from the sub-field code words for performing motion estimation separately for single sub-fields and that the apparatus has corresponding compensation blocks (dFCC) for calculating corrected sub-field code word entries and wherein the motion estimators and compensation blocks are used repetitively during a frame period for the single sub-fields.